Successful treatment of pure red cell aplasia with Orelabrutinib following major ABO-incompatible hematopoietic stem cell transplantation for acute myeloid leukemia: A case report.

Pure red cell aplasia (PRCA) is a severe complication following major ABO-incompatible hematopoietic stem cell transplantation (HSCT). Its pathogenesis is primarily attributed to the persistent production of anti-donor isohemagglutinins (anti-A/B antibodies) by residual host B lymphocytes and plasma cells. Clinically, this condition results in prolonged red blood cell (RBC) transfusion dependence and an increased risk of secondary iron overload. Currently, no standard therapy exists for this challenging complication, prompting evaluation of novel targeted agents. Here, we report a case of refractory PRCA in a patient with acute myeloid leukemia (AML) who underwent major ABO-incompatible HSCT (donor: A Rh+, recipient: O Rh+) and failed multiple prior interventions, including rituximab, cyclosporine, and intravenous immunoglobulin, before achieving durable remission with orelabrutinib, a next-generation Bruton's tyrosine kinase inhibitor (BTKi). To our knowledge, this represents the first documented use of orelabrutinib for PRCA in a patient who received HSCT for AML. Within four weeks of initiating therapy, the patient demonstrated a robust reticulocyte response, followed by sustained transfusion independence, which underscores the therapeutic potential of targeted BTK inhibition in this setting.